Superconducting materials for electronic devices may be created by forming films of suitable high temperature superconducting compounds on the surfaces of suitable substrate materials. The techniques are similar to those long used in the production of semiconductor films.
Precursors of the superconducting material are vaporized in a vacuum chamber by sputtering, ion beam sputtering, laser evaporation, electron beam heating or the like. The precursor materials travel through space to be deposited on a suitable substrate, usually chosen to encourage epitaxial growth of the HTSC material in a desired crystalline arrangement. The temperature of the substrate must be carefully controlled and this is achieved by mounting the substrate on some type of heating device. Many such substrate heaters are known in the semiconductor processing arts. However, the requirements of producing HTSC materials are far more demanding than those of making semiconductors. HTSC processing requires utilization of very high vacuums to reduce the chance for any high temperature equipment to cool itself which is also common in semiconductor processing. However, most currently known HTSC compounds require the introduction of oxygen in a very controlled way, at elevated temperatures and pressures. Thus, the substrate heater is exposed to a very strong oxidizing environment. The fabrication of good quality HTSC films requires very uniform heating of the substrate with variations of less than 2 degrees centigrade across the wafer even while operating at overall temperatures in the area of 900 degrees centigrade.
Precise control of the operating temperature is necessary since it is only in an optimum range of temperatures that the fine balance of several competing processes is maintained that determines the crystallization of the structure and the uptake of oxygen into the growing films. If conditions are not exactly controlled, contamination may result from reaction and interdiffusion between the substrate and the growing film. If the balance is not sustained, it can adversely affect the superconducting transition temperature, the width of the transition to zero resistance, and the critical current density. Prior art heaters have not as yet met these criteria.